渣油加氢空冷器铵盐结晶沉积特性预测方法

Prediction method of crystallization deposition characteristics of ammonium salt in residue hydrotreating air cooler

针对渣油加氢空冷器频繁出现的铵盐结晶沉积堵管问题,分析了空冷器铵盐沉积堵塞的机理,对加氢空冷器的铵盐结晶温度进行了预测;构建了空冷器翅片管束与风机空气侧的对流传热模型,结合Mixture多相流模型对翅片管内介质的流动及传热特性进行了研究,对空冷管束结晶沉积的高风险位置进行了预测,提出了流速、温度、腐蚀性介质气相摩尔分数及铵盐结晶速率等表征因素。结果表明:空冷器整体流场的平均温度及平均流速分布呈现大致相同的趋势,空冷器第一管排的正对法兰两侧处存在低流速区域及低温区域;随着相对入口管箱距离的增加,翅片管内多相流的平均温度不断降低,高温区域不断下移至管道底部部位;随着管内气相物质不断冷凝成为液相,管内多相流的平均流速不断降低,高/低流速区分层愈发显著;同时,随着温度的持续降低,管内NH_(3)在气相中的摩尔分率不断降低,而HCl的气相摩尔分率不断升高,铵盐结晶速率也随着温度的降低不断增大,并在靠近出口管箱附近达到最大值。通过对空冷翅片管的失效解剖分析,验证了铵盐沉积特性预测方法的准确性,可为石化企业加氢空冷器铵盐结晶风险与沉积位置的预测提供理论支持。

In view of the problem of the blockage of the ammonium salt in the residue hydrotreating air cooler due to frequent salt deposition,the mechanism of the deposition and blockage of the ammonium salt in the air cooler was analyzed,and the crystallization temperature of the ammonium salt in the hydrotreating air cooler was predicted.The convection heat transfer model between the finned tube bundle of the air cooler and the air side of fan was established.The Mixture multiphase flow model was used to study the flow and heat transfer characteristics of the media in finned tubes.The high risk location of crystallization deposition was predicted.The characterization factors such as flow rate,temperature,the mole fraction in the gas phase of corrosive medium and crystallization rate of ammonium salt were proposed.The results show that the average temperature and average velocity distribution of the overall flow field of the air cooler show roughly the same trend,and there are low velocity areas and low temperature areas on both sides of the opposite flange of the first tube row of the air cooler.With the increase of the distance from the inlet channel box,the average temperature of the multiphase flow in the finned tube decreases continuously,and the high temperature zone moves down to the bottom of the tube continuously.The average velocity of the multiphase flow in the tube decreases with the condensation of the gas phase into the liquid phase,and the stratification in the high/low velocity zone becomes more significant.At the same time,with the continuous decrease of temperature,the molar fraction of NH_(3) in the gas phase decreases continuously,while the molar fraction of HCl in the gas phase increases continuously.The crystallization rate of ammonium salt increases continuously with the decrease of temperature,and reaches the maximum near the outlet channel box.The accuracy of the prediction method for the deposition characteristics of ammonium salt was verified by the failure anatomy and analysis of air cooler finned tube,which can provide theoretical support for the prediction of crystallization risk and deposition location of ammonium salt in hydrotreating air coolers of petrochemical enterprises.